rich lee wrote:
Hello everyone,
Hello,
I am trying to read "mastering algorithm with perl" and below example has me
bit stuck.
I understand everything except these 2 lines
$low = $try + 1, next if $array->[$try] lt $word;
$high = $try -1, next if $array->[$try] gt $word;
Those two lines are short for:
if ( $array->[ $try ] lt $word ) {
$low = $try + 1;
next;
}
if ( $array->[ $try ] gt $word ) {
$high = $try - 1;
next;
}
I understand what it's doing but I am not sure how they are being ran.
For example, Let's say in one particular turn, $array->[$try] is greater
than $word...
I am trying to understand how it skips this line ---> $low = $try + 1, next
if $array->[$try] lt $word;
If $array->[$try] is greater than $word then it cannot be less than
$word, or equal to $word at the same time.
when I look at above 2 lines, it looks like they should be processed
sequentially. Meaning $low = $try + 1 should be processed everytime...and
$high=$try-1 should be
processed everytime....
No, only "if $array->[$try] lt $word" is processed every time.
In reality(after looking at the explanation), it should only lower or raise
when $array->[$try] is either less than(then it should raise the bottom) and
greater( should lower the top)
I think I am just not understanding the syntax on above 2 lines.. can
someone please describe it for me(or am i missing the precedence of the
relationship of the line??
$index = binary_search( \...@array, $word )
sub binary_search {
my ($array, $word) = @_;
my ($low, $high) = ( 0, @$array - 1 );
while ( $low <= $high ) {
my $try = int( ($low+$high)/2 );
$low = $try + 1, next if $array->[$try] lt $word;
$high = $try -1, next if $array->[$try] gt $word;
return $try; #we've found the word!
}
return; #the word isn't there
}
John
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annoyance to those of us who do. -- Isaac Asimov
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